PORTLAND, Maine — A portion of Baxter Boulevard will be closed for up to eight months starting Wednesday, as the Department of Public Services breaks ground on two underground stormwater conduits designed to reduce sewage overflow into Back Cove.

The stretch of the boulevard from Vannah Avenue to Bates Street was scheduled to be closed to all traffic beginning at 7 a.m., according to a City Hall press release. The roadway was originally slated to close last November, but the conduit project was rescheduled because of permitting delays.

Pedestrians will continue to have access to the trail system that borders the boulevard, and parking in Payson Park will be available for those wishing to use the trails.

The city suggested that motorists use Interstate 295, Brighton and Forest avenues, and Riverside Street as alternate routes.

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The concrete conduits, each with a capacity of 1 million gallons, are being installed under the boulevard and the park. When complete late this year, they still store a mix of wastewater that can then be sent to the Portland Water District’s treatment facility in the East End, instead of being discharged directly into Back Cove.

Currently, more than half of the city’s sewer system combines residential and industrial sewage and stormwater into a single drainage system. When the system is overloaded — for example, during heavy rainstorms — some of the untreated mixture flows into Portland waterways, and eventually into Back Cove, Casco Bay or the Fore River.

The city also has been grappling for two decades with a deteriorating system of sewer pipes, many of which were built of brick around the time of the Civil War. In November, the city announced it was negotiating with the U.S. Environmental Protection Agency over fines for past overflows.

Under federal order between 1993 and 2010, the City Council funded projects that reduced sewer overflow volumes 42 percent, from 720 million gallons to 420 million gallons annually. Those projects included $70 million of work to separate the stormwater and sewage systems.

More recently, the City Council approved a plan supporting $170 million of additional projects that would reduce sewer overflow volumes to 87 million gallons annually. That plan is set to begin in 2014.